Virtual Temperature

The virtual temperature is the temperature of dry air that would have the same density and pressure as the moist air. The virtual temperature allows meteorologists to take into account the fact that water vapor actually has a higher specific volume (size relative to its weight) than dry air. Thus, air with lots of water vapor in it is actually less dense than air with no water vapor in it.

Virtual Temperature allows one to compare densities of air at different temperatures and dew points. Air with high virtual temperatures is less dense than air with low dew point temperature, even if their actual temperatures are the same.